from typing import Optional


class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
class Solution:
    def mergeTwoLists(self, 
                      list1: Optional[ListNode], 
                      list2: Optional[ListNode]
                      ) -> Optional[ListNode]:
        dummy = ListNode()
        cur = dummy
        while list1 and list2:
            if list1.val <=list2.val:
                cur.next = list1
                list1= list1.next
                cur = cur.next
            else:
                cur.next =list2
                list2 = list2.next
                cur = cur.next
        
        while list1:
            cur.next = list1
            list1 = list1.next
            cur = cur.next
        
        while list2:
            cur.next =list2
            list2 = list2.next
            cur = cur.next
        
        return dummy.next



